1. Field of the Invention
This invention relates generally to a fiber hoop for supporting an optical fiber bundle and, more particularly, to a single piece, circular fiber hoop including a center mandrel and opposing side guards, where fiber optic cables are wound on the mandrel and optical connectors are mounted to the side guards, and where the fiber hoop has particular application for fiber optic cables providing optical signals for sensors in a power generator.
2. Discussion of the Related Art
High voltage generators for generating electricity as a power source are well known in the art. A power plant may include a gas turbine engine that rotates a shaft by combusting fuel and air in a combustion chamber to generate a working gas that expands across blades that rotate, and in turn causes the shaft to rotate. The shaft of such an engine is coupled to an input shaft of a high voltage generator that is mounted to a rotor having a special configuration of coils. An electrical current provided in the rotor coils generates a magnetic flux around the coils, and as the rotor rotates, the magnetic flux interacts with windings in a stator core enclosing the rotor, which generates a current flow in the windings
A typical high voltage generator includes an outer housing or frame comprised of structural steel including an internal bore in which the stator core and rotor are mounted. Often times, the outer frame is filled with hydrogen and pressurized for operation of the generator, where the pressurized hydrogen provides a good environment for cooling purposes. The stator core is typically a stacked assembly of several thousand laminate rings of a relatively thin ferrous material, such as iron or steel A group of the laminations are formed together during assembly of the generator and slid onto construction bolts extending along an inside surface of the internal bore of the frame The rotor is then rotatably mounted within the laminate rings It is critical that sensors are provided within the pressurized environment of the outer frame of a high voltage generator to measure operating conditions and detect failures. For example, a typical high voltage generator may include eight suitable sensors providing measurements for vibration, temperature, strain, etc.
In modern high power generators, these measurements are typically obtained using optical sensors, such as fiber Bragg grating (FBG) sensors, Rayleigh scattering sensors, etc, that employ a fiber optic cable. The analyzing devices that monitor the optical signals from the sensors are external to the generator frame and thus it is necessary to provide a penetration including a pressure seal at a suitable location within the frame through which the fiber optic cables can exit the frame without effecting the pressure environment therein. In one known design, the fiber optic cable including the sensor, sometimes referred to herein as a sensor cable, is optically coupled to another fiber optic cable, sometimes referred to herein as an analyzer cable, through a suitable fiber optic coupler within the pressure environment of the frame, where it is the analyzer cable that extends through the penetration and pressure seal to be coupled to the analyzing device. An end of the fiber optic cable including the optical sensor is positioned at the location where it is desired to take the particular measurement, and then the fiber is routed within the frame in a strategic manner so that it is less likely to be damaged to a location where the pressure seal is provided to gain access outside of the generator.
The fiber optic cable including the sensor is provided by the manufacturer of the sensor and comes in a set length, such as seven meters Typically, that length of the sensor cable is significantly longer than what is required to provide the optical sensor at the sensing location and optically coupled to the analyzer fiber at the location of the pressure seal Because it is not practical to have an installer reduce the length of the sensor fiber cable during assembly of the power generator, various techniques are employed in the art to bundle the optical fiber to confine the excess length of the cable.
In one known bundling technique, the excess fiber optic cable is freely wound into a loop having a diameter, for example, of 8-10 inches, so that bending of the fiber does not significantly affect the propagation of the optical signal therein. Particularly, once all of the fiber optic cables have been routed to the pressure seal location, then the installer will freely wind the excess fiber length of all of the fiber optic cables into a single free loop. The loop is then enclosed in a protective coating of a suitable material and is mounted to an inside wall of the frame. Requiring the installer to freely loop the excess fiber optic cables typically creates inconsistencies from loop to loop sometimes resulting in optical losses in the fiber as a result of loop configuration. Particularly, as the installer wraps the fibers into the loop, optical losses as a result of the fiber being bent typically occur, where those losses are not consistent from one loop to the next loop